Semiconductor manufacturing processes include, in obtaining a desired device structure, a process of film deposition on a substrate to be processed, that is, a silicon wafer (hereinafter, referred to as “a wafer”), and such film deposition process conventionally uses a sputtering apparatus.
This sputtering apparatus produces plasma in such a way dial: a sputtering gas that is an inert gas such as argon is introduced into a vacuum chamber in a vacuum atmosphere; and a target formed depending on the composition of a thin film to be formed on a substrate surface is made to cause glow discharge by being supplied with a predetermined electric power from a DC power supply or high frequency power supply. Then, ions, such as argon ions, of the inert gas ionized in the plasma collide with the target, and thereby atoms and molecules of the target are ejected from the target. These sputtered panicles adhere to and are deposited on the substrate surface to form the film. In this case, the substrate to be processed is positioned and held by substrate loading means disposed at a position opposed to the target.
As the substrate holding means, there is a known one including: a chuck main body having positive and negative electrodes; a conductive chuck plate having a rib portion capable of bringing a peripheral edge portion of a substrate into surface contact with the rib portion, and multiple supporting portions provided upright and arranged at predetermined intervals in an interior space surrounded by the rib portion; and a DC power supply configured to apply a DC voltage between the two electrodes (see patent Document 1, for example).
In addition, as a sputtering apparatus to form a predetermined thin film at a high bottom coverage ratio (a ratio of a film deposition rate on the bottom surface of a hole with respect to a film deposition rate on a surface around the hole) for a fine hold with a high aspect ratio, there is a known one in which: a target made of a metallic material such as Cu, Ta or Ti is used; sputtered particles generated by sputtering are ionized in plasma; and the ions of the spattered particles are attracted to and made incident on the substrate by applying a high frequency bias voltage to the substrate (see Patent Document 2, for example).
Here, a sputtering apparatus including the aforementioned substrate holding means holds a substrate by passing a current through the positive and negative electrodes. For this reason, the substrate surface is charged with free electrons in plasma, and thereby the potential of the substrate surface is shifted to the negative side. Moreover, when the high frequency bias voltage is applied to the substrate, ions having heavier mass than electrons cannot respond to a quick change in the alternating electric field. As a result, the substrate surface is charged with the electrons and thereby the potential of the substrate surface is shifted to the negative side. When the potential of the substrate is shifted to the negative side, ions of the inert gas in the plasma are also attracted toward the substrate, and a so-called reverse sputtering occurs in which a substance adhered to and deposited on the substrate surface is sputtered. An amount of reverse sputtering is variable depending on an atmosphere in the vacuum chamber and a sputtering duration in the sputtering operation. In ease where film deposition is performed on substrates conveyed to a position opposed to a target, thin films are formed on the substrate surfaces by controlling sputtering conditions such as the input power supplied to the target, and the sputtering duration. Even in such controlled deposition, if an amount of reverse-sputtered, substance (hereinafter, referred to as a reverse-sputtered amount) is large, for example, the films cannot be deposited with a desired film thickness, which causes a problem that the film thickness and even the film quality in some cases vary among the substrates.